The present invention relates to automation of longwall mining equipment.
The desire for increased automation of longwall mining equipment is considerable, inasmuch as manual monitoring and control of equipment operation requires a high degree of attention, experience, and relatively fast judgement.
The basic type of automated longwall mining system proposed in the prior art (see, e.g., "Bretby Broadsheet, July/September 1968, No. 44, pp. 3-4") is fully automatic and responds directly and immediately to changes in detected geological conditions. For example, the heights of the actual top and bottom boundary surfaces of a seam being worked are continually detected by isotopic nucleonic sensors or sensitized picks, capable of sensing the boundary surface between seam-coal and adjoining rock based upon the difference in properties of the two materials at the opposite sides of each boundary surface. If during a working trip of the power loader, it is for example detected that the true seam top height is higher than the top cut surface presently being cut, the upper cutting drum of the power loader is automatically raised, in direct and immediate response to the detection of this discrepancy. Thus, as the power loader travels along the length of the coal face, the cutting drums, but especially the upper one, are automatically adjusted in height, in continual immediate response to ongoing detection of true seam-top height. In this way, supposedly, the upper cutting drum will form a roof surface which is perfectly coincident with the rock-coal interface or, in the case where a coal roof is required, parallel to and spaced a constant predetermined distance from the rock-coal interface. The logic of proceeding in such a manner is clear; it is to maximize the amount of coal won and minimize the amount of contaminating rock being cut.
Such automatic, immediate-response control systems are suitable in geographical areas where the coal-rock interface is very well defined, continuous and relatively constant. However, in for example Western Germany, this is seldom the case. Instead, the coal-rock interfaces are typically discontinuous and irregular. In such areas, the use of an automatic, immediate-response control system is simply impossible, first because the system would respond to every sensed fluctuation in interface height and be in a continual state of overreaction, and second because an immediate automatic-tracking response to the sizable irregularities encountered could create roof and/or floor surfaces which the face conveyor, power loader and self-advancing roof-support system would be incapable of negotiating.
A partial solution to this problem is set forth in U.S. Pat. No. 4,008,921 to Czauderna et al. In that system, before any coal-winning work begins, mineralogical measurements are performed at a plurality of locations along the longwall passage, to determine the shape of the coal-rock interface. From the measured data, an interface-shape program is developed, either manually or by computer. The interface-shape program is then stored and used to control the heights of the upper and lower cutting drums during the first, and a plurality of subsequent trips. By comparison with the actual physical interface, the interface represented by the interface-shape program is well defined, continuous and smooth. The longwall mining system then rigidly adheres to the interface-shape program for a plurality of working strips, until such time as the program used has become stale, relative to the actual interface conditions being encountered. Then, a new set of measurements are taken, a new interface-shape program is established, and so forth.
This system is automatic, to the extent that there is negative-feedback control of the heights of the upper and lower cutting drums, relative to the heights commanded by the interface-shape program. If geological or operating conditions cause the development of improper transverse inclination, i.e., not corresponding to the preprogrammed transverse inclination of the interface-shape program, the system automatically adjusts cutting-drum height, to correct the inclination error. However, the automatic correction of cut-surface height and inclination errors is a correction relative to the preestablished interface-shape program, and is not a correction relative to feedback data from interface sensors such as used in the type of automatic, immediate-response system referred to earlier.
While the semi-automatic system of U.S. Pat. No. 4,008,921 thus constitutes a partial solution to the problem in question, the clear disadvantage of this semi-automatic system is the need to stop operation and establish a new interface-shape program as soon as the old one has grown stale. Stopping operation is troublesome in itself. Furthermore, because of the understandable desire to retain the old interface-shape program as long as tolerable, the program may indeed be quite stale during the last few working trips of its use. Clearly, this is far from optimum. On the other hand, as already stated, a system which directly responds to ongoing detection of changing interface conditions would not be operative for the geologies in question.